Question: 2 erasers cost $3.50. Which equation would help determine the cost of 11 erasers?
There are several equations that could help determine the cost, each with a slightly different approach. Let $x$ represent the unknown cost of 11 erasers. Since 11 erasers cost $x$ , we have the following proportion: $\dfrac{11}{x}$ We can write the fact that 2 erasers cost $3.50 as a proportion: $\dfrac{2}{\$3.50}$ The cost changes along with the number of erasers purchased, and so the two proportions are equivalent. $\dfrac{11}{x} = \dfrac{2}{\$3.50}$